How is a wave formed? Understanding swell and surf forecasts

Surfing

How is a wave formed? The surf report, the swell report, and surf forecasts are results of scientific studies and weather prediction models. In order to know what type of surf we will get in the next days, it's important to learn how waves are created.

Waves are mainly a product of the wind. It's the first step in the formation of surfable waves. Wind interaction on the surface of the ocean far from the coast can create some of the best waves on earth.

Local shore winds can also produce waves, but they usually destroy the quality of the breaking waves. Onshore winds are typically known for creating choppy and bumpy waves because they push in the direction of the wave, making them unstable.

In a way, offshore winds act as a sort of a counterbalance. Swell comes from miles away, and the ground wind works as a "pause-hold" effect on the wave face, pushing against it and allowing longer, unbreakable waves.

Low Pressure Systems | Good Waves for Surfing

In theory, low-pressure systems are responsible for creating good and strong waves. In deep low-pressure systems, wind speed is greater and more waves are generated by the power of the gusts.

The friction created by these winds helps to form energy waves that travel thousands of miles until hitting final obstacles; usually coastal areas.

If winds created in low-pressure systems keep blowing over the surface of the ocean for a long time, the swells will be bigger because energy from the wind is accumulated in the waves being produced.

Also, if low-pressure winds affect a vast area of the ocean, waves produced by the swell will have even more energy and power, resulting in really big ones.

From Ocean Waves to Surfing Waves | Sea Floor and Swell Obstacles

We've already analyzed the "birth" of swell and correspondent waves, but there's a significant distance to be traveled by those waves. Original oceanic waves may have to run a long journey until they reach continental beaches.

Along the way, until they are ridden by surfers, these waves will come into contact with other variables. The height of a wave when it is created is not the height of the waves that is ridden by a surfer.

Waves make their way through the ocean and are affected by variances in the ocean floor. When large volumes of water pass over higher sea floors, the overall energy of the swell is changed.

In one common instance, moving waves coming into contact with offshore continental shelves meet sustained friction resistance, and when these waves reach coastal areas in shallower water conditions, the swell has already lost intensity, energy and power.

But when waves travel without obstacles, through deep water regions, they tend to reach a beachfront with huge force. When waves reach shallow waters, they tend to slow down. Wavelength is shortened, and the crest of a wave grows, meaning that the wave height rises.

Bathymetry studies the underwater depth of the ocean floor and its changes over time. The bathymetric map has measured the highest and lowest depths of the sea floor over the entire planet.

Sea floor topography is important to have knowledge of. It helps captains and seamen worldwide avoid disasters and accidents with ships and line cruisers.

Sand Banks | Increasing the Wave Crest

Sand banks are always changing at beach breaks. This is why beach break wave quality is so variable and often unreliable. Sand ridges along the ocean floor, which rise near to the surface of the water, allow the formation of clear and localized wave peaks, from where surfers can take off on a ride.

A new sand bank typically means a new wave peak because swell hits the sandy obstacle and pumps the wave crest, allowing surfable waves. Other obstacles that can affect swell behavior are jetties, sunken boats, or natural or artificial reefs.

Created by wind, and influenced along the way by changes in sea floor topography, rainfall, tides, coastal backwash, currents and local winds, waves are a complex result of an amazing array of meteorological and geological variables.

Surf Forecasting | Wind and Wave Facts

1. Long-period waves tend to be larger and stronger2. Short-period waves are smaller and less energetic3. Wave period is the time between successive crests4. Wave frequency is the number of waves passing a point over a specific amount of time5. Large waves move quickly6. Small waves move slowly7. Low-pressure systems create a powerful swell8. Low-pressure systems are associated with rainy weather and cloudy skies9. High-pressure systems are associated with warm weather and clear skies10. Deep water coastlines deliver bigger waves11. Tsunamis cannot be surfed